1. Field of the Invention
The invention relates generally to thermal transmitting structures, and more particularly to a heat pipe having an operating fluid and a method for manufacturing the heat pipe.
2. Description of the Prior Art
Electronic components such as semiconductor chips are becoming progressively smaller, while at the same time heat dissipation requirements thereof are increasing. In many contemporary applications, a heat pipe is one of the most efficient systems in use for transmitting heat away from such components.
Referring to FIG. 4, a typical heat pipe 10 is a vessel that comprises a pipe 11, a wick 12, and a precise amount of liquid operating fluid 13. The wick 12 is a capillary structure, and is fixed to an inside wall (not labeled) of the pipe 11. The liquid operating fluid 13 is sealed in the pipe 11 and soaks the wick 12. One end of the heat pipe 10 is an evaporator section, and the other end of the heat pipe 10 is a condenser section. The evaporator section is disposed in thermal communication with an external heat source, while the condenser section is disposed in thermal communication with an external heat sink. Further, an adiabatic section connects the evaporator section to the condenser section, with heat being transmitted within the heat pipe 10 from the evaporator section to the condenser section through the adiabatic section.
An operating principle of the heat pipe 10 is as follows. Liquid operating fluid 13 is originally located in the evaporator section of the heat pipe 10. A heat source such as ambient hot air transmits heat 15 by conduction through the wall of the heat pipe 10 to the liquid operating fluid 13, and the temperature of the liquid operating fluid 13 rises. When the temperature of the liquid operating fluid 13 is equal to a temperature at which the liquid operating fluid 13 changes from the liquid state to a vapor state, the provision of additional heat 15 transforms the liquid operating fluid 13 into vaporized operating fluid 14. Vapor pressure drives the vaporized operating fluid 14 through the adiabatic section to the condenser section of the heat pipe 10. At the condenser section, the vaporized operating fluid 14 transmits the heat 15 absorbed in the evaporator section to a heat sink (not shown) located at the condenser section, and the vaporized operating fluid 14 is thereby transformed back into liquid operating fluid 13. Capillary action of the wick and/or gravity moves the liquid operating fluid 13 back to the evaporator section. The heat pipe 10 continues this cyclical process of transmitting heat 15 as long as there is a temperature differential between the evaporator section and the condenser section, and as long as the heat 15 is sufficient to vaporize the liquid operating fluid 13 at the evaporator section.
In order to ensure the effective operation of the heat pipe 10, the wick 12 must has good capillary performance, so that the operating fluid 13 can be distributed uniformly therethrough. U.S. Pat. No. 6,478,997 discloses a heat pipe adopting carbon fibers as a wick. The carbon fibers have high thermal conductivity and low cost. The size of the carbon fibers is not apparent from the disclosure. If the carbon fibers are large, the capillary performance of the wick 12 is likely to be poor. This retards the vaporized operating fluid being condensed back to its liquid state, and also retards the liquid operating fluid returning to the evaporator section. Any heat pipe adopting carbon fibers should not employ large fibers, otherwise poor thermal conductivity is likely.
Conventional heat pipes generally adopt pure liquids as their operating fluids. U.S. Pat. No. 5,947,193 discloses such kind of heat pipe. The heat pipe comprises a precise amount of operating fluid. The operating fluid is selected from the group consisting of pure alcohol, freon, water and acetone. However, for many applications, the thermal conductivities of these operating fluids are too low. The rate of heat transmission is too slow, and the operating efficiency of the heat pipe is unsatisfactory.
A new heat pipe which overcomes the above-mentioned problems is desired.